The present invention relates to a multi-mode magnetic recording system and multi-mode magnetic recording and playback system for a video tape recorder (VTR) and, more particularly, to a system for recording audio signals into tracks common to video signals and system for playing them back thereoutof.
As well known in the art, in a helical scan magnetic recording and playback apparatus (VTR), a plurality of rotary heads, such as two, are mounted on a drum or like rotatable member at an equal angular distance. A magnetic tape is wound around the rotary member over an angular range which may be a little over 180 degrees, for example. The rotary heads on the rotatable member are adapted to write video signals on the magnetic tape. Meanwhile, a stationary head is located in the path of travel of the magnetic tape so as to write audio signals thereon. During playback, the rotary heads read the video signals and the stationary head, the audio signals.
A current trend in the art of video tape recording is to extend a record and playback time. This, coupled with the demand for a higher utilization rate of the given area of a magnetic tape, is increasing the tendency toward the installation of two additional rotary heads to the above-mentioned two rotary heads and, accordingly, a lower tape transport speed added to a standard speed. At the same time, there is an increasing demand for higher quality in the playback of audio signals. Because the relative speed between the running tape and the stationary head for writing and reading audio signals is low, there arises a dilemmatic situation that a decrease in the running speed of the tape significantly limits the frequency characteristic of audio signals, compared to that of video signals which are written and read by the rotary heads, restricting high quality audio reproduction.
In light of this, there has been proposed a system which frequency multiplexes an audio signal to a video signal after converting the audio signal into a predetermined mode, and records the multiplexed signals on a magnetic tape by means of a video signal read and write head and reads them out of the magnetic tape. In accordance with such a system, because a rotary head writes and reads audio signals on and from a magnetic tape of which a relative scanning speed of the head is quite high, the audio recording and playback quality is far higher than the system which writes and reads audio signals by means of a stationary head with a standard tape speed.
In the proposed recording and playback system described above, an audio signal is subjected to at least frequency modulation and then frequency multiplexed to a video signal which may be made up of a frequency modulated luminance signal and a low range carrier color signal, the multiplexed signals being written and read by a common rotary head. This brings about a problem that beat occurs between the carrier frequencies causing interference (moire) pattern on the reproduced picture.
Also known in the art is a multi-mode magnetic recording and playback system which is furnished with a rotary head exclusive for audio signal recording. In this system, video signals are written on a magnetic tape providing a guard band between adjacent tracks, while audio signals are written in the tape by the exclusive rotary head on the guard band. The system, however, suffers from the drawback that because it is not constructed to keep the centers of the video and audio tracks in order with each other, any tracking error during playback allows, for example, a video head having a given azimuth angle to read audio signals written in the same azimuthal direction or allows an audio head having a given azimuth angle to read video signals of a same azimuthal direction, resulting in an increase of cross-talk.